Thousands of commuters suffered an appalling start to the week with three Tube lines either part suspended or running with delayed services.Problems still remain on the Circle, District and Hammersmith & City lines following a signal failure.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.